It is well known in the art of magnetic-tape sound recorders that the recording and reproducing frequency characteristics and the harmonic distorsion characteristics vary markedly with the bias current superposed on the recording signals supplied to the recording head of the sound recorder. Proper selection of the recording bias current is, for this reason, an essential requirement for achieving satisfactory recording and reproducing frequency characteristics in a magnetic-tape sound recorder. Since, however, the frequency response characteristics of a magnetic-tape sound recorder varies from one magnetic tape to another due to the difference between the respective recording and playback sensitivities of the tapes which may be of the same type or make, extreme difficulties have been encountered in achieving satisfactorily "flat" frequency response characteristics for all the magnetic tapes to be put to use on the sound recorder. The present invention aims at resolution of such a problem and contemplates provision of a magnetic-tape sound recorder incorporated with a computer-controlled device for automatically adjusting the signal level of the recording signal and the bias current to be superposed on the recording signal prior to recording and playback using a magnetic tape. More specifically, the present invention contemplates improvement of the apparatus disclosed in U.S. Patent Application Serial No. 096,265.